run away engine

[mramccm]

Hi Guys newbie here to this forum, 96 XP, 787

Changed out gray lines and cleaned Fuel selector valve, fuel filter, fuel pump, etc.

Started up engine and it went high RPM !!!

Hit stop switch ,, pulled safety lanyard,, nothing happened.

Shut off fuel selector nothing,

Now here is the weird thing, yanked off Ignition leads to plugs and engine just kept running as if it were a deisel.
Finally choked it to kill the engine.

After shut down, reestarted and it seemed to run normal.

What happened and why?

Has anyone ever heard of this before?

Chuck: confused:

 

[Bills86e]

No slack in accellerator cable. Common runaway.

They run away because they are too lean for the amount of fuel being put into the motor. They get too much air, and not enough fuel. 951 engines will run away even without air leaks or lean condition. They will run away if the idle speed is set too high. You must have slack in the throttle cable at the idle position, and to set the on-hose idle speed to 2800 rpm, 1400 or so in the water.
If the engine continued to run without the electrical system (i.e. the lanyard was removed), the fuel has to be getting ignited from somewhere. Likely you have some carbon deposits in the combustion chamber that are getting hot enough to ignite the fuel. Carbon deposits are very common in two stroke engines. In addition to rebuilding the carbs, I'd suggest decarboning the engine using your favorite method. You'll likely need to replace the plugs afterward, but you should do that annually anyway.

Ever hear the term "Glowplugging" the tip of the sparkplug gets red hot and ignites the fuel without electrical imput to the sparkplug.
This happens when the motor runs too lean of an air/fuel mixture. Too much air, not enough fuel. Fuel keeps the combustion temps within a certain safe range. Take away the fuel just a little bit and you have a glowplugging motor that revs to the moon ! :cheers: Bills86e

 

[mramccm]

Thanks for the quick reply bill. I am reallly surprised at this being so common.
I think I did not go far enough in cleaning and or rebuilding my carbs. That is my next step.

Chuck